According to the Royal Shakespeare Company, David Tennant will be undergoing back surgery for a slipped disc.
Tennant has been experiencing back problems for some time, and has recently been unable to perform in the most recent productions of Hamlet, where he has played the title role some 60 times.
Now it seems he will not be returning to the role at all, since he was already scheduled to finish his run in the production on January 10th, and it seems unlikely he would be able to do so so quickly after surgery.